1. Field of the Invention
The present invention relates to a bifunctional optically active liquid crystal intermediate compound useful as an intermediate for synthesizing a liquid crystal or polymeric liquid-crystal compound, and a process for preparing it.
More particularly the present invention is concerned with a liquid crystal intermediate compound used as an optically active component in a chiral nematic liquid crystal or a chiral polymeric liquid-crystal compound and a chiral smectic liquid crystal or a chiral polymeric liquid-crystal compound which are characterized as being optically active.
2. Related Background Art
Hitherto known liquid-crystal devices include a device that employs the twisted nematic liquid crystal as disclosed in M. Schadt and W. Helfrich, Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal, "Applied Physics Letters", Vol. 18, No. 4, pp. 127-128 (Feb. 15, 1971). This twisted nematic liquid crystal, however, has a problem of crosstalk occurring at the time of time division drive using a matrix electrode system having a high density of picture elements, and hence has a restriction in the number of the picture elements.
There has been also a limit in its use as a display device because of a slow electric field response and poor visual-field angle characteristics. This liquid crystal has another problem that a very complicated process is required for the formation of a thin-film transistor for each picture element and moreover a display device with a large area can be produced with difficulty.
For eliminating the disadvantages of such a conventional liquid-crystal device, Clark and Lagewall have proposed to use a liquid-crystal device comprised of a bistable element (see Japanese Patent Application Laid-Open No. 56-107216 and U.S. Pat. No. 4,367,924). Commonly used as this liquid crystal comprised of a bistable element is a ferroelectric liquid crystal comprised of a chiral smectic C phase (Sm*C) or H phase (Sm*H).
This ferroelectric liquid crystal (FLC) exhibits spontaneous polarization, and hence has a very quick response and moreover can produce a bistable state with memory performance. In addition, it has superior visual-field angle characteristics, and hence can be considered to be suited as a material for display with a large capacity and a large area. When, however, a liquid crystal cell is actually formed, it is difficult to achieve a monodomain over a large area, and a technical problem has remained unsettled in making a display device with a large screen.
As a countermeasure to such problems, it is reported in U.S. Pat. No. 4,561,726 to utilize an interfacial surface energy so that a monodomain of a ferroelectric smectic liquid crystal can be prepared by an epitaxial method.
The monodomain thus prepared, however, can not be stable by nature and may easily turn into a multidomain by the application of pressure or thermal stimulation. This makes it difficult to accomplish large-area display.
On the other hand, a polymeric liquid-crystal device has been proposed as a device that can be readily fabricated as a device and is suited for large-area display. The device as disclosed in U.S. Pat. No. 4,239,435 is known as a device driven by the application of an electric field.
What is disclosed in British Patent No. 2,146,787 is known as a device that can be addressed using a laser beam. Japanese Patent Application Laid-Open No. 62-14114 discloses a device that can be addressed using a thermal head or the like.
Of these devices, the device employing a chiral nematic polymeric liquid crystal containing an optically active group performs display and recording in a wavelength-selective state by the use of spiral selective scattering of the polymeric liquid crystal.
Display units that employ such polymeric liquid-crystal devices are suited for highly detailed display with large areas, but are disadvantageous in that they have too low response speed to be suitable for animations or for uses in which rewriting is performed at a high speed.
Various studies are made for the purpose of eliminating the above disadvantages. As one of the results thereof, a ferroelectric polymeric liquid crystal is reported in N. A. Plate et al., Polymer Bulletin, 12, p.299 (1984). This ferroelectric polymeric liquid crystal can be readily formed into a device, e.g., readily formed into a film, and is suited for large-area display. This can greatly improve response speed compared with a conventional polymeric liquid crystal, and can be expected to be put into practical use.
In the manufacture of such a ferroelectric polymeric liquid crystal, it is essential to use an optically active compound. For example, an optically active alcohol or an optically active carboxylic acid is used as the optically active compound.
Of these optically active compounds, a monofunctional optically active liquid crystal intermediate is the same as the one used in a low-molecular liquid crystal, and can be used in a terminal side chain of a polymeric liquid crystal. It, however, can not be used in a spacer flexible chain of a main-chain type polymeric liquid crystal or in a side-chain spacer flexible chain of a side-chain type polymeric liquid crystal. Hence, the polymeric liquid crystal produced using a monofunctional optically active liquid crystal intermediate has the disadvantage that it must be limited in structure.
On the other hand, bifunctional optically active liquid crystal intermediate compounds hitherto known are few in kind and limited in structure, and hence there has been the disadvantage that the liquid crystal or polymeric liquid crystal produced using the intermediate compound is also limited in structure for its molecular designing. In addition, the bifunctional optically active liquid crystal intermediate compound is expensive and has allowed no free selection on its length (or the number of carbon atoms) when used as a flexible spacer chain of a polymeric liquid crystal.
Moreover, none of the conventional bifunctional optically active liquid crystal intermediate compounds have a large permanent dipole moment in the vicinity of an asymmetric atom. Hence, they exhibit a small spontaneous polarization when formed into ferroelectric polymeric liquid crystals or polymeric liquid crystals, and have had the disadvantage that a high-speed response can be achieved with difficulty.